Case study: Managed realignment of sea walls can enhance coastal protection provided by natural habitats and save costs


What was the problem?

As a result of climate change the coasts of England and Wales are coming under increasing threat from erosion and flooding. To protect human settlements, coastal defences such as sea walls were built, however it is now increasingly recognised that these defences cause the degradation or loss of coastal and intertidal habitats and the ecosystem services they provide, in particular flood protection. The security provided by ‘hard’ engineered defences encourages infrastructure and settlements to develop closer to the coast which increases the risk of damage and consequently the need for protection.

What can be done to solve it?

According to the Department for Environment, Food & Rural Affairs of the United Kingdom government (DEFRA), "maintaining the current line of defence (hold the line)", "limited intervention", "doing nothing" and "managed realignment" are among the policy options to be considered in coastal and flood risk management.

When investigating coastal protection strategies with a time horizon beyond 25 years, managed realignment of sea walls can be an economically efficient policy for coastal and flood risk management, instead of maintaining sea walls at the current line of defence (hold-the-line strategy).

In order to decide for a certain site whether managed realignment is economically efficient or not, the different realignment scenarios need to be compared.

Which ecosystem services were examined? And what methods were applied?

Managed realignment creates space for new intertidal habitats, including tidal mud flats and salt marshes that provide a number of ecosystem services including coastal protection and flood defence. These areas provide productive habitats for plants, invertebrates and molluscs, and they are very important fish nursery areas and feeding, breeding and roosting areas for birds.

Salt marshes dissipate wave energy and provide the first line of defence against tides and waves, particularly during storms. Hence, they reduce the capital and maintenance costs of fixed flood defences. Intertidal habitats also act as sinks for pollutants and carbon and provide recreational opportunities. Thus, managed realignment has both, conservation and coastal defence benefits.

What policy uptake resulted from examining the ecosystem services?

Whether managed realignment is the policy of choice or not depends on the location. A shorter defence line, lower height of embankments and the beneficial effect of intertidal habitats for reducing wave energy can reduce maintenance costs. In addition the ecosystem services provided by newly created intertidal habitats beyond coastal protection have to be considered (e.g. carbon sequestration or as habitat for endangered species). However, the value of land that needs to be protected (e.g. infrastructure, housing or farmland) is an important factor which varies locally.

An analysis carried out in 2002 by the DEFRA listed 151 coastal sites in England and Wales where defence line retreat has been adopted as a strategy for coastal protection. From these sites 41% were classified as actual managed realignment sites and 59% as limited intervention sites.

Information prepared within the project "Non-governmental sector participation in the international conference" EU Biodiversity strategy implementation "" financed by Latvian national budget-funded program "Support for public participation in the Latvian Presidency of the Council of the European Union implementation" and administered by the Society Integration Foundation.